Radio frequency oscillators are widely used in a variety of applications, such as for instance multi-mode multi-band applications. Radio frequency oscillators usually comprise resonator circuits as frequency selective elements, wherein the resonator circuits comprise inductors and capacitors. The inductors and capacitors are connected to be in resonance at a specific resonance frequency. For providing a high tuning range of a radio frequency oscillator, different approaches are applied.
An exemplary approach to provide an increased tuning range is to employ two separate radio frequency oscillators having separate resonator circuits and using high frequency multiplexers, which can lead to an increased power consumption and noise floor and can demand for a large die area. In L. Fanori et al., “A 2.4-to-5.3 GHz dual core CMOS VCO with concentric 8-shape coils,” ISSCC Dig. Tech. Papers, pp 370-372, 17-21 Feb. 2013, a topology having separate resonator circuits is described.
A further exemplary approach is based on switching between even and odd resonance modes of a high-order LC resonator circuit within a radio frequency oscillator. A separation of resonance peaks in the different modes can be achieved, however, leading to a large size of the LC resonator circuit. In G. Li. et al., A Distributed dual-band LC oscillator based on Mode Switching,” IEEE TMTT, vol. 59, no. 1, pp. 99-107, January 2011, a topology using mode switching is described.
Common radio frequency oscillators providing a high tuning range suffer from an increased noise floor and/or an increased size, in particular when implemented as radio frequency integrated circuits (RFICs) on semiconductor substrates.